In the construction of metal substrates for catalytic converters, catalytic mufflers for automobiles, fume abatement activities in general, and the like, often times it is desired to provide a metal substrate that is elliptical in cross section. In the past, it has been extremely difficult to accurately and readily construct such elliptical cylindrical metal substrates (also called ovals or racetracks). However, it has been found, according to the present invention, that when particularly shaped and dimensioned mandrels are employed, elliptical cylindrical metal substrates may be easily fabricated.
The metal substrates according to the present invention are formed from "metal substate material". That term, as used in the present specification and claims, refers to material having a large amount of void volume. Conventionally, such material comprises a planar metal foil sheet with a corrugated foil sheet disposed thereon. The two sheets may be attached together or may be separate until being formed into the elliptical cylindrical metal substrate in which case they are wrapped together with a planar foil between each corrugated foil layer. While the term "metal substrate material" refers to a variety of materials with high void volume that are suitable for formation into an elliptical cylindrical metal substrate, alternating corrugated and planar foils is a suitable illustrative embodiment thereof. As an alternative to one planor and one corrugated foils, two sheets of corrugated foil can be wrapped together, providing their corrugations are aslant so as to prevent nesting, to form an elliptical cylindrical metal substrate.
According to the method of the present invention, generally elliptical cylindrical metal substrates having a major diameter D, a minor diameter d, and a depth H are formed by practicing the steps of: providing a plate mandrel having a generally rectangular cross section of length L and thickness T and having a depth approximately H; affixing a first end of a web of metal substrate material having a width H to a surface of the plate mandrel; wrapping the metal substrate material web around the mandrel until a substantially uniform thickness X is provided of metal substrates surrounding the mandrel to provide a generally elliptical cylinder with depth H; providing a second end of the metal substrate material web; and affixing the second end of the web to an underlying portion of the formed elliptical cylinder. The approximate dimensions L and T of the plate mandrel are determined before wrapping by using the equations 2X+L=D and 2X+T=d. After calculation of the approximate dimensions, the optimum dimensions L and T are empirically determined, to take into account deformation of the metal substrate material that will occur at the edges of the plate mandrel during wrapping. Wrapping may be accomplished in a number of ways, but most suitably by affixing the plate mandrel to a rotating component, and rotating the mandrel with respect to a roll of metal substrate material to wind the material from the roll around the mandrel.
Also according to the present invention, a generally elliptical cylindrical metal substrate is provided having a major diameter D, minor diameter d, and depth H, comprising: a plate having a generally rectangular cross section of length L and thickness T and a depth H, located at the center of the substrate and extending between and terminating generally at the foci of the elliptical cylindrical metal substrate; a plurality of wrappings of metal substrate material disposed around the plate and having a substantially uniform thickness X; and means for maintaining the wrappings and plate integral. The plate is preferably made of high temperature oxidation resistant alloy and the wrappings of metal substrate material comprise alternate layers of planar metal foil and corrugated metal foil. Spot welds comprise the means for maintaining the wrappings and plate integral, affixing the first end of the metal substrate material wrappings to the plate and affixing a second end of the wrappings to a previous, interior wrapping.
It is the primary object of the present invention to provide a simple method for making acceptable elliptical cylindrical metal substrates, and to provide an elliptical cylindrical metal substrate that is suitable for catalyzing and functions well in fume abatement applications in general. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.